Oil and gas reservoirs are underground formations of rock containing oil and/or gas. The type and properties of the rock vary by reservoir and also within reservoirs. For example, the porosity and permeability of a reservoir rock may vary from well to well within a reservoir. The porosity is the percentage of pore volume, or void space, within the reservoir rock that can contain fluids. The permeability is an estimate of the reservoir rock's ability to flow or transmit fluids. Other reservoir properties that affect production of a well include reservoir pressure, temperature, hydrocarbon percentage and skin effect for the well.
Reservoir properties are often determined or inferred from down hole well logs. Well logging data includes data from sonic logging, gamma ray logging, electric logging, and magnetic resonance imaging (MRI) logging. MRI provides environmentally safe logging that is unaffected by variations in matrix mineralogy. MRI is widely used to estimate the bulk volume of fluids of a reservoir. MRI allows fluid filled pore space to be partitioned into static and dynamic quantities, those fluids that will be held to the rock and fluids that will be produced. Permeability can be computed from the relationship between moveable and irreducible fluid volumes.
Estimating production of oil, gas and/or byproducts from a well is highly interpretive. A common method for confirming production for a well is a short term production test such as a swab test in which a tool or seal is moved in the well bore to reduce pressure. In response to the reduced pressure, reservoir fluids flow into the well bore and towards the surface for measurement and testing.